The present invention is directed to electrosurgical systems, apparatus and methods for removing an implanted object from a patient""s body, and specifically to systems and methods for the removal of implanted endocardial or epicardial pacemaker leads or transvenous defibrillation leads from a patient""s heart and the venous paths thereto.
Various types of pacemaker leads and their electrodes are introduced into different chambers of the heart, including the right ventricle, right atrial appendage, the atrium and the coronary sinus, although the majority of pacemaker leads are implanted in the right ventricle or appendage thereof. These flexible leads provide an electrical. pathway between a pulse generator, connected to the proximal end of the lead, and the heart tissue, which is in contact with the distal end or electrode of the lead. Electrical pulses emitted by the pacemaker travel through the pacemaker lead and stimulate the heart to restore healthy heart rhythms for patient""s whose hearts are beating irregularly.
Pacemaker leads usually comprise an insulating sleeve that contains a coiled conductor having an electrode tip at the distal end. This electrode tip is often placed in contact with the endocardial or myocardial tissue by passage through a venous access, such as the subclavian vein or one of its tributaries, which leads to the endocardial surface of the heart chambers. The electrode tip is held in place within the trabeculations of myocardial tissue. The distal ends of many available leads include flexible tines, wedges or finger-like projections which project radially outward to help prevent dislodgment of the lead tip from the cardial tissue.
Once an endocardial lead is implanted within a heart chamber, the body""s reaction to its presence furthers its fixation within the heart. Shortly after placement, blood clots form about the flanges or tines due to enzymes released in response to the irritation of the cardial tissue caused by the electrode tip. Over time, fibrous scar tissue eventually forms over the distal end, usually in three to six months. In addition, fibrous scar tissue often forms, at least in part, over the insulator sleeve within the venous system and the heart chamber.
Endocardial leads occasionally malfunction, due to a variety of reasons, including lead block, insulation breaks, breakage of the inner helical coil conductor, etc. In addition, it is sometimes desirable to electronically stimulate different portions of the heart than that being stimulated with leads already in place. Due to these and other factors, a considerable number of patients may eventually have more than one, and sometimes as many as four or five, unused leads in their venous systems and heart. These unused leads often develop complications, such as infection, septicemia, or endocarditis. In addition, unused leads may entangle over time, thereby increasing the likelihood of blood clot formation, which may embolize to the lung and produce severe complications or even fatality. Further, the presence of unused leads in the venous pathway and inside the heart may cause considerable difficulty in the positioning and attachment of new endocardial leads in the heart.
Conventional techniques for removing unused pacemaker leads are also associated with serious risks. Standard mechanical traction and, more often, intravascular mechanical countertraction are the methods most commonly used at present (notably the system manufactured by Cook Pacemaker Corporation). External mechanical traction involves grasping the proximal end of the lead and pulling. This process is repeated daily, usually a few millimeters of the lead are removed from the patient each day, with progress monitored by chest radiography. Internal mechanical traction is accomplished by exerting traction (manual or sustained) on the lead via a snare, forceps or other retrieval catheter that has grasped the lead within the venous system. These techniques, however, can cause disruption of the heart wall prior to release of the affixed lead tip, causing fatality, or other complications, such as lead breakage with subsequent migration, myocardial avulsion or avulsion of a tricuspid valve leaflet. Moreover, lead removal may further be prevented by a channel of fibrotic scar tissue and endothelium surrounding the outer surface of the lead body or insulator sleeve at least part way along the venous pathway. Such channel scar tissue inhibits withdrawal of the lead because it is encased within the scar tissue. Continual pulling or twisting of the proximal free end of the lead could cause rupturing of the right atrial wall or right ventricular wall.
Intravascular countertraction is accomplished by applying traction on the lead while countering this traction by the circumference of dilator sheaths advanced over the lead. While maintaining sufficient traction on the lead to guide the sheaths, a pair of sheaths is advanced over the lead toward the myocardium to dislodge scar tissue from the lead. If insufficient tension is placed on the lead, however, the method is no longer countertraction but reduced to external traction with the aforementioned risks. In addition, misdirected countertraction along the lead body may tear the vein or heart wall.
In an effort to overcome some of the problems associated with mechanical traction and intravascular countertraction lead removal methods, lasers have been developed for extracting pacemaker leads. In some of these techniques, catheters having laser fibers at their distal end are advanced over the pacemaker lead to the site of attachment. The laser fibers are then energized to separate the lead from the fibrous scar tissue. These devices are described in U.S. Pat. Nos. 5,423,806, 5,643,251, 5,514,128 and 5,484,433. The standard laser light source for these devices is the xenon-chloride excimer laser, which is commercially available from Spectranetics Corporation of Colorado Springs, Colo.
Conventional electrosurgery methods have not been successful in removing pacemaker leads. One of the factors which appears to create the greatest impediment to electrosurgical removal of pacemaker leads is scar tissue. Scar tissue exhibits much lower thermal conductivity and electrical conductivity than normal (e.g., myocardial) tissue. Since conventional electrosurgery generally relies on the conduction of electrical currents through the target tissue being cut or vaporized, conventional electrosurgery has failed to remove this scar tissue. In fact, previous attempts to use conventional electrosurgery methods to remove pacemaker leads have resulted in current flow and thermal effects in the xe2x80x9chealthyxe2x80x9d tissue surrounding the scar tissue mass, but not in the scar tissue mass itself. As a result, the targeted scar tissue was not affected and the lead was not removable.
The present invention is directed to systems, methods and apparatus for removing implanted objects from a patient""s body, particularly implanted objects attached to fibrous scar tissue. The systems and methods of the present invention are particularly useful for removing implanted endocardial or epicardial pacemaker leads or transvenous defibrillation leads from a patient""s heart.
Methods of the present invention comprise positioning one or more electrode terminal(s) adjacent an implanted object attached to tissue and applying a sufficient high frequency voltage difference between the electrode terminal(s) and one or more return electrode(s) to detach the implanted object from the tissue. The high frequency voltage is typically sufficient to ablate or remove a portion of the tissue between the implanted object and the remaining tissue so that the implanted object can then be removed without pulling or tearing the patient""s tissue. In preferred embodiments, an electrically conductive fluid, such as isotonic saline or conductive gas, is delivered to the target site around the pacemaker lead to substantially surround the electrode terminal(s) with the fluid. Alternatively, a more viscous fluid, such as an electrically conductive gel, may be delivered or applied directly to the target site such that the electrode terminal(s) are immersed within the gel during the procedure. In both embodiments, high frequency voltage is applied between the electrode terminal(s) and one or more return electrode(s) to remove at least a portion of the tissue.
In one aspect of the invention, an electrosurgical catheter is advanced to a position within the thoracic cavity adjacent a portion of a pacemaker lead that is affixed to heart tissue. Preferably, the catheter is advanced over the pacemaker lead, i.e., using the pacemaker lead as a guidewire, to facilitate this positioning step. Once the distal end of the catheter reaches a blockage, or a portion of the lead that is attached to fibrous scar tissue, a high frequency voltage difference is applied between one or more electrode terminal(s) at the distal end of the catheter and one or more return electrode(s) to remove the scar tissue around the lead. Depending on the configuration of the distal end of the catheter, the electrode terminal(s) may be rotated, oscillated or otherwise manipulated to facilitate the removal of tissue between the lead and the heart. The catheter is then advanced further along the lead until it reaches another blockage caused by fibrous scar tissue, and the process is continued until the catheter reaches the distal tip of the lead in the myocardium. At this point, the distal tip may be severed from the rest of the lead, or pulled out of the myocardial tissue in a conventional manner. Alternatively, the catheter may be energized and advanced through the myocardial tissue to form an annular channel around a portion of the distal tip. If the distal tip includes flanges or tines, these tines may be severed with the electrical energy, and the remainder of the distal tip removed from the myocardial tissue.
In a specific configuration, the fibrous scar tissue is removed by molecular dissociation or disintegration processes. In these embodiments, the high frequency voltage applied to the electrode terminal(s) is sufficient to vaporize an electrically conductive fluid (e.g. gel or saline) between the electrode terminal(s) and the tissue. Within the vaporized fluid, a ionized plasma is formed and charged particles (e.g., electrons) are accelerated towards the tissue to cause the molecular breakdown or disintegration of several cell layers of the tissue. This molecular dissociation is accompanied by the volumetric removal of the tissue. The short range of the accelerated charged particles within the plasma layer confines the molecular dissociation process to the surface layer to minimize damage and necrosis to the underlying tissue. This process can be precisely controlled to effect the volumetric removal of tissue as thin as 10 to 150 microns with minimal heating of, or damage to, surrounding or underlying tissue structures. A more complete description of this phenomena is described in commonly assigned U.S. Pat. No. 5,683,366, the complete disclosure of which is incorporated herein by reference.
The present invention offers a number of significant advantages over current techniques for removing pacemaker leads. For one thing, the scar tissue around the pacemaker lead is precisely ablated before removing the lead, which minimizes or eliminates the risks associated with mechanical traction and countertraction, such as disruption of the heart wall, lead breakage with subsequent migration and the like. In addition, the ability to precisely control the volumetric removal of tissue results in tissue ablation or removal that is very defined, consistent and predictable. The shallow depth of tissue heating also helps to minimize or completely eliminate thermal damage to the heart. In particular, since the mechanism for removing or ablating the scar tissue does not rely primarily on electrical current flow through the scar tissue, the low electrical conductivity of the scar tissue (relative to the adjacent heart tissue) does not effect the removal of this tissue. In addition, since the electrical current primarily flows back to the return electrode through the electrically conductive fluid, current flow into healthy heart tissue is minimized. Moreover, since the present invention allows for the use of electrically conductive fluid (contrary to prior art bipolar and monopolar electrosurgery techniques), isotonic saline may be used during the procedure. Saline is the preferred medium for irrigation because it has the same concentration as the body""s fluids and, therefore, is not absorbed into the body as much as other fluids.
Apparatus of the present invention comprise a catheter shaft having a flexible body with a proximal end portion and a distal end portion having a distal opening. The catheter shaft has an inner lumen coupled to the distal opening and sized to accommodate a pacemaker lead, usually about 0.2 to 10 mm diameter and preferably about 0.5 to 5 mm in diameter. The catheter body has one or more electrode terminal(s) on the shaft at the distal end portion, and a connector extending through the body for coupling the electrode terminal(s) to a source of high frequency electrical energy.
The apparatus will preferably further include one or more fluid delivery element(s) for delivering electrically conducting fluid to the electrode terminal(s) and the target site. The fluid delivery element(s) may be located on the catheter, e.g., one or more fluid lumen(s) or tube(s), or they may be part of a separate instrument. Alternatively, an electrically conducting gel or spray, such as a saline electrolyte or other conductive gel, may be applied the target site. In this embodiment, the apparatus may not have a fluid delivery element. In both embodiments, the electrically conducting fluid will preferably generate a current flow path between the electrode terminal(s) and one or more return electrode(s). In an exemplary embodiment, the return electrode(s) are located on the catheter and spaced a sufficient distance from the electrode terminal(s) to substantially avoid or minimize current shorting therebetween and to shield the return electrode(s) from tissue at the target site. Alternatively, the return electrode(s) may comprise a dispersive pad located on the outer surface of the patient (i.e., a monopolar modality).
In a specific configuration, the apparatus includes a plurality of electrically isolated electrode terminals extending from the distal end of the catheter shaft. The electrode terminals are each mounted within an electrically insulating support member, and spaced peripherally around the distal opening of the catheter body. In these embodiments, the catheter may include a single, annular return electrode located proximal of the distal opening, or a plurality of electrode terminals mounted to the support members proximal of the electrode terminals. The latter embodiment has the advantage that the electric currents are confined to a distal region of the catheter body, which may facilitate advancement of the catheter through fibrous scar tissue. In this embodiment, the catheter body also includes one or more fluid delivery lumens spaced peripherally around the central lumen for delivering electrically conductive fluid to the electrode terminals. In addition, the catheter body will preferably include one or more suction lumens spaced peripherally around the central lumen, and suitably coupled to an external suction source for aspirating fluid, tissue and/or gaseous products of ablation (e.g., non-condensible gases) from the target site.
In one embodiment, the catheter includes a lateral port, opening or slit proximal to the distal end of the catheter (typically about 0.5 to 10 cm), and sized for receiving the pacemaker lead therethrough. In this embodiment, the pacemaker lead is loaded through the distal opening into the inner lumen of the catheter, and out through the lateral port so that the lead only extends through a distal end portion of the catheter body. This side port loading feature makes it easier to advance the catheter body over the pacemaker lead, and provides the physician with more control of the distal end portion. For example, this enhanced control allows the physician to rotate the distal end of the catheter relative to the pacemaker lead and the fibrous scar tissue to facilitate the removal of an annular channel of scar tissue around the lead (e.g., the electrode terminals are energized and rotated to ablate or remove an annular channel of tissue). In this embodiment, the connectors for the electrode terminal(s) and the return electrode(s) are preferably flat tape wires that extend around the periphery of the distal end portion, and around the lateral port to the proximal end of the catheter body.